when all you have had to worry about the entire season is beating your teammate rather than worrying about a half-dozen other drivers and cars, it makes for one of the easiest WDCs in history IMO, because it means you can concentrate all of your energies on beating only one opponent.
Depends on the teammate.
When a driver has the best car and a vastly inferior teammate, that is the clearly the easiest path to the title. When you've got to battle a similarly matched teammate in equal machinery race in race out, the title becomes increasingly difficult to achieve for both parties.
Nico and Lewis would have a good laugh if someone told them either had an "easy" path to the championship.
The battle in 2013 between the two drivers in the top car was simply embarrassing.